API-571 Exam Dumps

API RP 571 on HTHA states:

''Acoustic emission testing is not currently a proven or reliable method for identifying HTHA in refinery components.''

''HTHA typically occurs internally, not as surface blisters, and is not limited to welds. Austenitic (300 series) stainless steels are generally resistant at normal refinery conditions.''

(Reference: API RP 571, Section 4.2.1.3 -- High Temperature Hydrogen Attack)

Thus, option A is the most accurate statement.

Comprehensive and Detailed Explanation From Exact Extract:

According to API RP 571, carbon steel exhibits a minimum corrosion rate in sulfuric acid at concentrations around 65--70 wt% due to formation of a protective iron sulfate film.

When sulfuric acid concentration drops below approximately 65%, this protective film becomes unstable and corrosion rates increase dramatically.

Referenced Documents (Study Basis):

API RP 571 -- Section on Sulfuric Acid Corrosion

API RP 571 notes in the context of Hydrochloric Acid Corrosion in overhead condensers:

''Titanium is highly resistant to low pH acidic aqueous phases, including hydrochloric acid formed during condensation in overhead systems.''

''Stainless steels like 316 and 410 are not suitable in the presence of free chlorides at low pH and elevated temperatures.''

(Reference: API RP 571, Section 4.3.3.3 -- Hydrochloric Acid Corrosion)

Thus, Titanium is the preferred alloy under the described acidic and high-temperature conditions, making option B correct.

Galvanic corrosion occurs when two dissimilar metals are electrically connected in the presence of an electrolyte such as brackish water or seawater. The rate and severity of galvanic corrosion depend on:

The relative position of the metals on the galvanic series (potential difference)

Area ratio between anode and cathode

Conductivity of the electrolyte

API RP 571 explains:

''The more active (anodic) metal in the galvanic couple corrodes preferentially. The more noble (cathodic) metal is protected.''

''The greater the difference in potential between the two metals, the more aggressive the galvanic reaction.''

''Aluminum is highly anodic compared to steel. In seawater or brackish conditions, aluminum will corrode rapidly when electrically coupled to steel, especially if the aluminum surface area is small relative to the steel.''

(Reference: API RP 571, Section 4.3.5.1 -- Galvanic Corrosion)

Referring to the galvanic series presented in your table:

Aluminum is much higher (more anodic) than steel.

This makes aluminum the sacrificial metal in such a pair.

This is not the case for brass-to-nickel or cast iron-to-Ni-Resist, which are much closer together on the galvanic scale.

Therefore, among all the listed pairs, Aluminum coupled to Steel creates the most significant galvanic potential difference and is most likely to result in galvanic corrosion in brackish or seawater service.

Correct Answer: B

API RP 571, under Organic Acid Corrosion, highlights:

''Corrosive organic acids in overhead systems are those that condense at temperatures above the water dew point. These acids condense independently of water and can form highly concentrated corrosive films.''

''When acids condense first, they aggressively corrode carbon steel prior to any water wash mitigation.''

(Reference: API RP 571, Section 4.3.3.9 -- Organic Acid Corrosion)

Hence, option D correctly identifies the most aggressive corrosion scenario.